In order to improve
electrical machinery
Quality, in recent years, motor noise has been included as one of the quality assessment indicators, especially for situations where the operating environment of the motor is in close contact with people, motor noise has become a very important assessment requirement.
In order to control the noise of asynchronous motors, in addition to selecting appropriate stator and rotor slot combinations during design, inclined slots can be used to reduce the electromagnetic noise of the motor. However, further experimental verification is needed to determine the appropriate slope of the groove.
In general, the inclination of the rotor slot of an asynchronous motor can be taken as one stator tooth pitch, which can basically meet the requirements. But in order to further improve motor noise, it is necessary to explore the optimal slot slope, which requires a lot of calculation and verification.
From the perspective of production and manufacturing, the production and processing of straight slot motors are relatively simple, but when necessary, the stator slots or rotor slots need to be twisted. Twisting the stator slots is relatively difficult, so in most cases, skewing the rotor slots is necessary. The skewing of rotor slots is generally achieved by machining skewed keyways on the shaft. For more advanced enterprises, spiral punching is used in the rotor core manufacturing process.
The causes and avoidance measures of electromagnetic noise
Motor noise has always been a difficult problem to solve, mainly caused by electromagnetic, mechanical, and ventilation reasons. Electromagnetic noise in asynchronous motors is caused by the interaction of harmonic magnetic fields established by the stator and rotor currents in the air gap, resulting in electromagnetic force waves that cause the yoke of the iron core to vibrate, forcing the surrounding air to vibrate. The main reason is due to improper slot fitting, eccentricity of the stator and rotor, or small air gap.
Electromagnetic noise is caused by changes in time and space, and by the magnetic pulling force acting between the various parts of the motor. Therefore, for asynchronous motors, the reasons for the formation of electromagnetic noise include:
The radial force wave of the air gap magnetic field causes radial deformation and periodic vibration of the stator and rotor.
The radial force waves of high-order harmonics in the air gap magnetic field act on the iron core of the stator and rotor, causing them to undergo radial deformation and periodic vibration.
The deformation of stator core with different order harmonics has different natural frequencies, and resonance occurs when the frequency of radial force waves is close to or equal to a certain natural frequency of the core.
The deformation of the stator causes vibration in the surrounding air, and most of the electromagnetic noise is load noise.
When the iron core is saturated, the component of the third harmonic is increased, causing an increase in electromagnetic noise.
The slots of the stator and rotor are all open, and there are many “slot opening waves” generated under the action of the fundamental magnetic potential in the air gap magnetic field. The smaller the air gap, the wider the slot, and the greater their amplitude.
To avoid this problem, effective measures should be taken during the product design stage, such as selecting a reasonable magnetic flux density, selecting appropriate winding types and associated circuits, increasing the number of stator punching slots, reducing the harmonic distribution coefficient of the stator winding, appropriately processing the air gap between the stator and rotor of the motor, selecting slot matching between the stator and rotor, and adopting rotor inclined slots.